David R. Hershey wrote:
>=20
> My guess would be that tannins are involved. Tannins are phenolic polym=
ers
> used to tan leather and which give tea its characteristic color. You co=
uld
> try staining concrete with tea to see if you can duplicate the effect.
> Denture cleanser commercials often try to remove tea stains.
>=20
> Taiz and Zeiger's Plant Physiology text describes the role of tannins a=
s
> feeding deterrents to herbivores.
>=20
> *********************************************************************
> David R. Hershey
>=20
> Snail mail: 6700 Belcrest Road #112, Hyattsville, MD 20782-1340
>=20
> Adjunct Professor, Biology/Horticulture Dept.
> Prince George's Community College, Largo, MD 20772-2199
>=20
> Email: dh321 at pgstumail.pg.cc.md.us>=20
> *********************************************************************
>=20
> On 11 Nov 1997, Dr. David Starrett wrote:
>=20
> > Plant-edders,
> > Walking across campus I notice the familair leaf stains on concrete
> > sidewalks. Some are very good images and show perfect leaf outline a=
nd
> > even major venation. I asked my Plant Phys class how they occur.
> > Now, I need to make sure I have an answer. This doesn't occur with=
green
> > leaves. I am assuming that water is leaching some pigments, tannins,=
etc
> > out of the leaf. Either chlorophyll isn't soluble, doen't stain, or
> > remains within a living leaf. What is it that is staining the concre=
te?
> > It is apparently water-soluble. On a hill, the stain smears to the
> > downhill side, with streaks often maintaining leaf width.
> > Anyone have some good answers I can relay to my students to maintai=
n my
> > front as a knowedgable Plant Physiologist.
> >
> >
> > ***********************************************************
> > * Dr. David Starrett *
> > * Biology Department, MS 6200 *
> > * Southeast Missouri State University *
> > * Cape Girardeau, MO 63701 *
> > * Ph: 573-651-2382 *
> > * Fax: 573-651-2223 *
> > * Email: dstarret at biology.semo.edu *
> > * URL: http://biology.semo.edu/web/starrett/starrhpg.html *
> > * *
> > ***********************************************************
> >
I spent last summer on a tributary of the Rio Negro in Brazil. The
acids that
produced the "leaf stains on concrete" mentioned by David Starrett are
responsible for
the "black water" rivers of tropical rain forests. Tropical black water
rivers and streams
occur in areas of sandy soils--the sand serving as a tea strainer,
holding the leaf litter
back while allowing the leachant to filter into the streams. Some of the
black water
streams look very black, like strong tea, while others are more of an
amber color. The pH
of the streams that I=92ve tested were around 4.2-5.4. Quite acid,
considering the amount of
rainfall in these rain forests. The leaves and seed pods--especially
some of the
Lecithedacea seed pods--when placed in a cup of water quickly produced a
dark colored
tea.
I have several articles of clothing that have been indelibly stained by
leaves that
managed to settle on them or by seed pods that were placed purposefully
in a pocket.
Bleaching with chlorine bleach only darkened the stain initially--that
surprised me when I
first saw it--and subsequent bleachings have not managed to lighten the
stains. While in
the jungle I used chlorine bleach both to purify my drinking water and
to remove body
odor from clothing hand-washed in the =93black waters=94. It was next to
impossible to get
the clothes clean but I wanted them to at least smell =93clean=94. When I
added the chlorine
bleach to the dark tea-like water it would immediately darken. My guess
is that there are
compounds in the acids of the tropical leaf litter that react with the
chlorine in a different
way than Lipton tea does. I=92m not much of a coffee drinker but I drink
enough black tea
that I need to remove tea stains occasionally form my clothes and a very
dilute chlorine
wash does the trick. So, you can imagine my surprise when the chlorine
bleach in my
camp wash water darkened the rain forest stains.
Papers that I have read refer to both tannic and humic acids as being
responsible
for the stains. I=92m a plant ecologist not a physiologist so I=92m not s=
ure
what the difference
between tannic and humic acids is--can anyone help me out in that area.
I have assumed
that tannic acid is one of many humic acids but I have been guessing and
don=92t know for
sure. =20
I don=92t think pouring tea onto concrete would produce a stain but
setting down a
fresh, wet tea bag might.=20
It is interesting that a green leaf does not stain--at least to the
same intensity--that
a brown leaf does. What compounds are formed by the decomposition of
chlorophyll and
other substances found within green leaves? And can electrophoresis or
thin layer
chromatography be accomplished on tea as it is on chlorophylls. I ran
into a German
scientist on the Rio Cueiras--I don=92t remember his particular
discipline--that was
attempting to do electrophoresis on the black water rivers. I was in my
canoe and he on a
river boat so I didn=92t get to visit with him long--but he claimed that
he was not successful
in conducting electrophoresis on black water rivers. Has anyone
attempted this before?
Until Later,
Ivan Williams
Stafford High School
Stafford, TX